This
website deals with the Yellow-legged Gull taxon michahellis, which
is a common migrant from July to December in NW Europe. After extensive expansion
of the breeding population during the last three decades, it nowadays can
be found breeding in Belgium, the Netherlands and Britain in mixed couples
with both Herring Gull (argenteus) and Lesser Black-backed Gull (graellsii).
There are subtle differences between the populations from the
Mediterranean, Atlantic coast of Portugal and Morocco and from the islands
in the Atlantic. Most pronounced differences can be found in the taxon atlantis,
now regarded as full species by some authors.